The three-dimensional (3D) integration of two or more semiconductor structures can produce a number of benefits to microelectronic applications. For example, 3D integration of microelectronic components can result in improved electrical performance and power consumption while reducing the area of the device footprint. See, for example, P. Garrou et al., “The Handbook of 3D Integration,” Wiley-VCH (2008).
The 3D integration of semiconductor structures may take place by the attachment of a semiconductor die to one or more additional semiconductor dice (i.e., die-to-die (D2D)), a semiconductor die to one or more semiconductor wafers (i.e., die-to-wafer (D2W)), as well as a semiconductor wafer to one or more additional semiconductor wafers (i.e., wafer-to-wafer (W2W)), or a combination thereof.
Often, the individual semiconductor structures (e.g., dice or wafers) may be relatively thin and difficult to handle with equipment for processing the semiconductor structures. Thus, so-called “carrier” dice or wafers may be attached to the actual semiconductor structures that include therein the active and passive components of operative semiconductor devices. The carrier dice or wafers do not typically include any active or passive components of a semiconductor device to be formed. Such carrier dice and wafers are referred to herein as “carrier substrates.” The carrier substrates increase the overall thickness of the semiconductor structures and facilitate handling of the semiconductor structures (by providing structural support to the relatively thinner semiconductor structures) by processing equipment used to process the active and/or passive components in the semiconductor structures attached thereto that will include the active and passive components of a semiconductor device to be fabricated thereon. Such semiconductor structures that will ultimately include the active and/or passive components of a semiconductor device to be fabricated thereon, or that will ultimately include the active and/or passive components of a semiconductor device to be fabricated thereon upon completion of the manufacturing process, are referred to herein as “device substrates.”
The bonding techniques used in bonding one semiconductor structure to another semiconductor structure may be categorized in different ways, one being whether a layer of intermediate material is provided between the two semiconductor structures to bond them together, and the second being whether the bonding interface allows electrons (i.e., electrical current) to pass through the interface. So called “direct bonding methods” are methods in which a direct solid-to-solid chemical bond is established between two semiconductor structures to bond them together without using an intermediate bonding material between the two semiconductor structures to bond them together. Direct metal-to-metal bonding methods have been developed for bonding metal material at a surface of a first semiconductor structure to metal material at a surface of a second semiconductor structure.
Direct metal-to-metal bonding methods may also be categorized by the temperature range in which each is carried out. For example, some direct metal-to-metal bonding methods are carried out at relatively high temperatures resulting in at least partial melting of the metal material at the bonding interface. Such direct bonding processes may be undesirable for use in bonding processed semiconductor structures that include one or more device structures, as the relatively high temperatures may adversely affect the earlier formed device structures.
“Thermo-compression” bonding methods are direct bonding methods in which pressure is applied between the bonding surfaces at elevated temperatures between two hundred degrees Celsius (200° C.) and about five hundred degrees Celsius (500° C.), and often between about three hundred degrees Celsius (300° C.) and about four hundred degrees Celsius (400° C.).
Additional direct bonding methods have been developed that may be carried out at temperatures of two hundred degrees Celsius (200° C.) or less. Such direct bonding processes carried out at temperatures of two hundred degrees Celsius (200° C.) or less are referred to herein as “ultra-low temperature” direct bonding methods. Ultra-low temperature direct bonding methods may be carried out by careful removal of surface impurities and surface compounds (e.g., native oxides), and by increasing the area of intimate contact between the two surfaces at the atomic scale. The area of intimate contact between the two surfaces is generally accomplished by polishing the bonding surfaces to reduce the surface roughness up to values close to the atomic scale, by applying pressure between the bonding surfaces resulting in plastic deformation, or by both polishing the bonding surfaces and applying pressure to attain such plastic deformation.
Some ultra-low temperature direct bonding methods may be carried out without applying pressure between the bonding surfaces at the bonding interface, although pressure may be applied between the bonding surfaces at the bonding interface in other ultra-low temperature direct bonding methods in order to achieve a suitable bond strength at the bonding interface. Ultra-low temperature direct bonding methods in which pressure is applied between the bonding surfaces are often referred to in the art as “surface assisted bonding” or “SAB” methods. Thus, as used herein, the terms “surface assisted bonding” and “SAB” mean and include any direct bonding process in which a first material is directly bonded to a second material by abutting the first material against the second material and applying pressure between the bonding surfaces at the bonding interface at a temperature of two hundred degrees Celsius (200° C.) or less.
Carrier substrates are typically attached to device substrates using an adhesive. Similar bonding methods may also be used to secure one semiconductor structure that includes active and/or passive components of one or more semiconductor devices therein to another semiconductor structure that also includes active and/or passive components of one or more semiconductor devices therein.
Semiconductor dice may have electrical connections that do not match the connections on other semiconductor structures to which they are to be connected. An interposer (L e., an additional structure) may be placed between two semiconductor structures or between any semiconductor die and a semiconductor package to reroute and align appropriate electrical connections. The interposer may have one or more conductive traces and vias used to make proper contact between the desired semiconductor structures.